Polymers which are both amine-functional and carry hydroxyl groups (so-called hydroxy-amino polymers) are increasingly of interest in some fields of application, especially in the field of the polyurethane industry. The reason for this is that the presence of two different types of functional groups, namely the amine functionalities and the hydroxyl groups, enables novel property and processing profiles to be achieved. For example, combining the amino groups, which are significantly more reactive towards isocyanate groups, with the less reactive hydroxyl groups gives rise to the possibility of influencing the progress of curing processes over time in a desirable manner, which has hitherto not been possible or has been possible to only a limited extent in the presence of only one type of the above-mentioned isocyanate-reactive functional groups.
In general, the amino functionality of hydroxy-amino polymers can be introduced into macromolecules by the addition of primary amines or ammonia to low-electron double bonds, for example of the (meth)acylate type. The addition of amines to (meth)acrylate-group-containing polymers, inter alia to (meth)acrylate-group-containing polyethers, is known per se; such processes are mentioned, for example, in U.S. Pat. No. 5,739,192 A1, U.S. Pat. No. 5,597,390 A1, US 2005/0171002 A1, DE 196 16 984 A1, DE 195 08 308 A1, WO 2010/090345 A1, JP 2009/22753 A1 and JP 04089860 A1.
By contrast, the obtainment of the precursor compounds comprising the low-electron double bonds in the prior art is either not described or takes place via condensation reactions that proceed according to the laws of statistics, for example by the esterification of acrylic acid with difunctional polyethers or the reaction of acryloyl chloride with difunctional polyethers.
A common feature of all the described processes is that the introduction of double bonds into the precursor compounds of the hydroxy-amino polymers takes place at the expense of the number of hydroxy functions. Accordingly, these processes do not allow the original hydroxy functionality, which in the case of polyether molecules is generally given by the functionality of the starter molecules used to prepare the polyethers, to be retained during the introduction of the amino functions.
Processes as are described, for example, in U.S. Pat. No. 4,874,837 A1 solve this problem in part by reacting mixtures of maleic anhydride and further anhydrides with the hydroxy groups of low molecular weight polyether polyols, converting the resulting acid groups of the semiesters back into hydroxy groups by addition of alkylene oxides, and introducing the amine function by addition of amino alcohols comprising primary or secondary amino groups or diamines comprising primary or secondary amino groups at the reactive double bonds of the hydroxy maleate.
A structural disadvantage of the hydroxy-amino polyether esters prepared in that manner is that the hydroxy groups and the amino groups are at a fixed and small distance of from 6 to 7 covalent bond lengths from one another and only one amino group can be introduced per hydroxy group. This situation can be shown schematically as follows:
                where R=polyether radical, R1, R2=radicals (hydrogen or alkyl) on the nitrogen atom, and R3=radical (hydrogen or alkyl on the alkylene oxide used to convert the acid groups into hydroxy groups)        
The two above-mentioned products of the Michael addition of the amine to the double bond are present in more or less equal parts, yielding a mixture of polymers with 6 and 7 bond lengths between the hydroxy group and the amino group.
U.S. Pat. No. 5,554,687 discloses a process in which α,β-unsaturated dicarboxylic acids or their anhydrides are first esterified by polyhydric alcohols or alkylene oxides to give an unsaturated “polyol polyester prepolymer”. In the case of maleic anhydride as the α,β-unsaturated dicarboxylic acid, the esterification is preferably to be carried out in the presence of morpholine as isomerisation catalyst. The specification does not mention further catalysts for the esterification process. In the presence of morpholine (an aminic catalyst), maleic anhydride reacts with alkylene oxides such that precisely one alkylene oxide structural unit is incorporated between two maleic anhydride structural units. When ethylene oxide is used as the alkylene oxide, there is thus ultimately obtained a polyester as from the reaction of maleic acid with ethylene glycol.
The “polyol polyester prepolymer” (a) is then reacted in a second step with a polyoxyalkyleneamine (b) in a weight ratio (a)(b) of from 0.8 to 50 to give an amine-containing polyester resin. There are disclosed as polyoxyalkyleneamines (b) polymers of polyether blocks with amino end groups, for example H2N—CHXCH2—[OCH2CHX]n—NH2, wherein X represents hydrogen or an alkyl group having from 1 to 18 carbon atoms and n is a natural number from 2 to 70. The terminal amino groups are added to the double bonds of the polyol polyester prepolymer. There are thus ultimately obtained crosslinked polyester resins in which the polyester chains are linked together via polyamino bridges. A process for the preparation of hydroxy-amino polymers in the sense of amino-group-containing poly(ether)ester polyols is neither described in nor rendered obvious by U.S. Pat. No. 5,554,687. Moreover, the process of U.S. Pat. No. 5,557,687 is subject to the same limitations as U.S. Pat. No. 4,874,837 A1 in relation to the structure of the chain ends. The distance between the terminal hydroxy group and the first amino group can here likewise be a maximum of 7 covalent bond lengths.
Accordingly, the object of the present invention was to provide a process for the preparation of hydroxyl-amino polymers which on the one hand permits the creation of hydroxy-amino polymers having a distance of more than seven covalent bond lengths between the amino functionality and the hydroxy functionality; on the other hand, the possibility of incorporating more than only one amine group per OH group into the polymer is to be opened up, this process is further to be simple to apply and, moreover, is to avoid as far as possible the formation of secondary products, such as, for example, transesterification products, so that working up of the process products is generally not necessary.